1. Field of the Invention
The present invention relates to a semiconductor light emitting device.
2. Description of the Related Art
Recently, a light emitting device, such as a light emitting diode (LED) having a luminance which has been increasingly improved, has been employed as a light source of a display, a lighting system, or a vehicle, and white light having good efficiency can also be implemented therein by using phosphors (or a fluorescent material) or combining colors. In order to implement an LED having this purpose, a device must have a low operational voltage and a high luminance and luminous efficiency.
The luminous efficiency may be divided into internal luminous efficiency and external luminous efficiency. Internal luminous efficiency is related to a defect of a semiconductor material constituting a light emitting device, while external luminous efficiency, which denotes the efficiency of light emitted from the semiconductor material to an external environment, is related to total internal reflection resulting from the difference between a refractive index of the semiconductor material and that of a material constituting the environment surrounding the light emitting device.
The most general method, among methods for implementing a white LED, is performing wavelength conversion by using a yellow phosphor in a blue LED to combine blue light and yellow light to thus implement a white light source. This method is greatly affected by the efficiency of the phosphor layer in implementing white color.
The structure of the white LED using a general phosphor layer is manufactured in the form of a package, and an LED is die-bonded to a lead frame structure by using an adhesive resin, and an upper portion of the LED has a filler made of a composite resin such as silicon, epoxy, or the like, molded therearound. In this case, in order to implement white-colored light, phosphor powder is mixed with the molding filler, which is then molded in the LED-adhered lead frame package.
In a white LED package, a portion of blue light radiated from a blue LED is transmitted, while the remaining light collides with the phosphor included in the filler to excite the phosphor to radiate yellow light, and the blue light and yellow light are mixed to produce white light. This structure, however, is disadvantageous, in that a path difference is made for light to reach an external surface of the package, resulting in a failure to obtain uniform light, and also, non-uniformity of the phosphors included in the filler may degrade the color gamut.